1. Field of the Invention
The present invention relates to valves and more particularly relates to butterfly type valves operated between open and closed positions by actuators.
2. Prior Art
So-called butterfly type valves have long been used for controlling the flow of various kinds of fluids in many different applications. One relatively common area of usage of such valves is in automotive vehicles driven by liquid cooled internal combustion engines and in which butterfly valves have been used to govern the flow of engine coolant through heat exchangers known as "heater cores" which function to heat air circulated in the vehicle passenger compartments. In this and other generally similar applications it is essential that the butterfly valve function to effectively seal against passage of fluid when in its closed position. Accordingly, many prior art butterfly valve constructions have employed a butterfly valve member positioned in a valve housing defining through flow passage for the fluid with the butterfly valve having a resilient periphery sealingly engageable with the surrounding valve housing wall when the valve member is in its closed position.
In many applications the butterfly valves are opened and closed in response to a remotely sensed condition such as air and/or liquid temperature, and in such circumstances it is common to provide an actuator of some sort for shifting the valve member between open and closed positions in response to changes in the sensed condition. Examples of valves constructed in this general fashion are illustrated by U.S. Pat. Nos. 3,857,406; 3,568,975; 3,675,681; 2,544,520; and 4,176,823.
In the butterfly valve assemblies illustrated by the U.S. Patents referred to above, the butterfly valve is operated between its open and closed positions by a fluid pressure operated actuator. In the disclosures of these patents the actuator is operated by differential air pressure applied to a piston or diaphragm which is in turn connected to the butterfly valve by a force transmitting linkage. The piston or diaphragm is also acted upon by a spring which actuates the valve to its open position in the absence of a differential pressure force acting on the piston or diaphragm.
In automotive vehicle applications it is commonplace to utilize the vacuum pressure in the engine intake manifold as a source of operating pressure for valve actuators of the type referred to. When one side of the piston or diaphragm is communicated with the engine intake manifold while the opposite side is exposed to atmospheric air pressure, the resultant differential air pressure acting on the piston or diaphragm moves the piston or diaphragm against the force of the spring and shifts the valve member to its closed position. The degree of vacuum pressure present in the engine intake manifold thus determines the magnitude of the valve closing force. This vacuum pressure varies widely depending upon operating conditions of the engine. Thus it is necessary to design the actuator so that the valve can be tightly closed against fluid flow even when the engine intake manifold vacuum is quite small (i.e. close to atmospheric pressure). As a result, when engine manifold vacuum levels are high, the valve actuators are capable of exerting a substantial excess amount of closing force on the already closed valve.
Excessive valve closing forces have led to failures of otherwise well constructed, functional valves. When a valve is in its closed condition and the engine is operated under various load and speed conditions, the closed valve is, in effect, cranked by varying forces while in its closed position and when the valve member is formed with a resiliently deformable periphery for sealing purposes, the valve tends to become jammed in its closed position. The cyclical cranking forces also tend to cause spalling of the resilient valve members which results in the valve members eventually failing to seal against the valve housing when in their closed positions.
Moreover, many valves of the type referred to have to be constructed by positioning the butterfly valve member within a surrounding valve body and then fixing the valve member to its operating shaft. Fixing the valve member to its shaft in situ is sometimes accomplished by spot welding and sometimes by cold forming a driving connection between the shaft and valve. Examples of these assembly techniques are disclosed, respectively, by U.S. Pat. Nos. 3,568,975 and 4,176,823. These kinds of force transmitting connections between valve member and shaft are adequately strong to assure opening and closing of the valves but have not always had sufficient strength to resist excessive valve closing forces without breaking.
In many valves the driving connection between the actuator linkage and the valve member shaft is also a relatively light duty connection which can be rendered ineffective by the application of excessive valve closing forces. It has become a common practice, particularly in the automotive industry, to test the valves by applying closing forces substantially greater than those expected to be encountered during use to determine whether the valves jam or the driving connections fail. Such testing results in the failure of many valves which are otherwise readily capable of operating satisfactorily in the absence of excessive closing forces.